122 Electrical Power Systems Technology
the earth was formed. When this magma comes close to the crust of the
earth, possibly through a rupture, a volcano could be formed and erupt.
Magma could also cause steam vents, like the ones at the “Geysers” area
in California. These are naturally occurring vents that permit the escape
of the steam formed by the water that comes in contact with the under-
ground magma. A basic geothermal power system is shown in Figure 5-2,
and the understructure for such a system is illustrated in Figure 5-3.
In the 1920s, an attempt was made to use the Geysers area as a power
source, but the pipelines were not able to withstand the corrosive action of
the steam and the impurities in it. Later, in the 1950s, stainless steel alloys
were developed that could withstand the steam and its impurities, so the
Pacific Gas and Electric Company started development of a power system
to use the heat from within the earth as an energy source. The first gener-
ating unit at the Geysers power plant began operation in 1960. At present,
more than 500 megawatts of electrical power are available from the gener-
ating units in the Geysers area.
In the geothermal system, steam enters a path (through a pipeline or
a vent) to the surface of the earth. The pipelines that carry the steam are
constructed with large expansion loops, causing small pieces of rock to be
Figure 5-2. Drawing of a basic geothermal power system.